The increasing requirements of television sets in terms of quality of the displayed images, and the increasing requirements of transmitting devices in terms of amplitude of the frequency bands used during transmission have made the techniques for transmitting video sequences very important. Use of digital transceiving systems has made possible splitting of a frame of a picture into a matrix of numerical values representing the intensities of the video components of each pixel of a frame. This allows processing of the picture by computers. The possibility of treating a picture as a matrix of numbers, and as a bitstream, offers the possibility of coding pictures to facilitate transmission and to improve the quality of displayed images.
Systems for coding video digital sequences are based on the recognition of several properties of pictures. Among such properties, a particular importance is the detection of the character progressive or interlaced of the pictures, and the detection of the motion of the objects. When these properties are known, it is possible to compress the picture making most efficient their transmission in terms of used frequency band, and most satisfactory in terms of their display quality.
Several techniques of motion estimation and detection of the progressive or interlaced content, i.e., interlaced progressive detection (IPD) of digital video sequences are known. Such techniques are disclosed in U.S. Pat. No. 5,734,420, and patents WO 99/20040, EP-A-0917363, EP-A-0944245, EP-A-0979011, EP99830545.2, and EP98830689.0. These patents are incorporated herein by reference in their entirety, and are assigned to the assignee of the present invention. The methods disclosed in the above mentioned documents operate on the bit values representing the video components of single pixels. This requires a computational complexity that makes them inappropriate for low cost applications.
A frame according to the PAL standard is composed of 720*288=207,360 pixels. Methods operating on each pixel are rather burdensome or impose simplifications that reduce the quality of the displayed picture. Methods of elaborating a bitstream of video digital sequences operating on groups of pixels (macroblocks) to reduce the computation complexity are generally used for low cost applications.
More precisely, there is a need for a method of elaborating data of digital video sequences that provides the following advantages while operating on groups of pixels. These advantages permit recognition of the processed picture as a progressive or interlaced picture with a reduced number of calculations. There should be a reduction in the amount of calculated motion estimations while preserving quality and efficiency of the compression. The quality of displayed pictures are enhanced for the same compression efficiency and the same amount of calculations performed during the motion estimation.